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Microscopical examination of Portland cement clinker
May, I943.]
NATIONAL BUREAU O1: ~TANDARDS NOTES.
527
made in the grades and standard sizes in order to keep a balanced relation to the veneer grades produced, and to prevent a critical shortage in those grades and sizes of plywood most commonly needed for construction purposes. The major changes made in the standard are the elimination of the grades " G o o d 2 Sides" and " G o o d I S i d e " and the addition of a new grade " S o u n d I S i d e " for moistureresistant stock. Also, a considerable reduction was made in the n u m b e r of standard thicknesses and widths. The present edition of the standard covers detail requirements for six grades of "Moisture-Resistant" type and seven grades of "Exterior T y p e " Douglas fir plywood, as well as tests for those two t y p e s of bonding. For those unfamiliar with the product, a chart is included, showing the types and grades that are generally suitable for a long list of uses, and a section covering nomenclature and definitions. Printed copies of CS45-42 are obtainable from the Superintendent of Documents, Government Printing Office, Washington, D . C . The price is IO cents. MICROSCOPICAL
EXAMINATION OF PORTLAND CEMENT CLINKER.
In tile microscopical examination of portland cement clinker by the metallographic method, a prismatic phase which is readily etched by water is frequently observed. A report on the nature of this phase is presented by William C. Taylor in the April Journal of Research (RPI536). This prismatic material has been observed only in relat i v e l y rapidly cooled clinkers containing K20 or Na20, or both. However, the results of a series of phase equilibrium studies show that K2SO4 and K20.23CAO. I2SIO2 are the only compounds containing K20 that may exist when a mixture of K20, CaO, MgO, A1203, Fe203, SiO2 and SO~, in the proportions occurring in portland cement clinker, is heated and cooled under equilibrium conditions. Neither of these compounds has properties similar to those of the prismatic phase. The results of microscopical examinations by o t h e r investigators on commercial clinkers were analyzed, and these results indicated that a very close chemical relationship existed between the prismatic phase and 3 C a O .A1,O~.
528
N A T I O N A L B U R E A U OF STANDARDS N O T E S .
[J. F. 1.
Accordingly, the relation of the prismatic phase to the system K20.~aCaO. I2SiO2-CaO-sCaO-3AI=O3, and to other systems involving K20, was studied. The phase in question was found to have no range of real stability, and was produced only u n d e r conditions of r a p i d cooling. The observed thermal and compositional requirements for its formation suggest that it may be a metastable form of 3CaO.AI203 and monotropic with respect to the stable, isotropic, rectangular 3CaO'AI203. The exact composition of the prismatic phase was not established definitely because of certain experimental difficulties, which are outlined in the report. That portion of K20 combined as K2SO4 in clinker was found to have no effect in inducing the formation of the prismatic material. In conclusion, the conditions necessary for the formation of the prismatic phase are briefly set forth and it is recommended that this phase be referred to as "prismatic 3CaO.AIsOs" instead of the indefinite term, "prismatic dark interstitial material." M O D U L U S OF E L A S T I C I T Y OF C O N C R E T E .
In a recent investigation at the Bureau, Rudolph C. Valore, Jr., and Jason C. Y a t e s observed the gain in dynamic modulus of elasticity, E, of concretes made with various brands of normal, white, and high-early-strength portland cements, cured in various ways, over periods up to 635 days. They also determined the effect of calcium chloride admixtures upon this modulus over the same periods of t i m e . Two groups of 4 by 4 by 3o inch prisms were cast from a concrete proportioned I : 2 : 4 by weight and with a water content of 6~ gallons per bag of cement. In each group, for each of 8 standard, t high-early-strength, and 2 white portland cements, triplicate specimens were cast for each calcium chloride admixture content (I, and 2 per cent. by weight of cement) and for p lain concrete. Initial determinations of dynamic E were made on one group of specimens 24 hours a f t e r casting; the specimens were then placed in a moist room at 7o°F. Additional determinations were made thereafter up to.27o days, after which the specimens were placed in dry storage at constant temperature
NATIONAL BUREAU O1: ~TANDARDS NOTES.
527
made in the grades and standard sizes in order to keep a balanced relation to the veneer grades produced, and to prevent a critical shortage in those grades and sizes of plywood most commonly needed for construction purposes. The major changes made in the standard are the elimination of the grades " G o o d 2 Sides" and " G o o d I S i d e " and the addition of a new grade " S o u n d I S i d e " for moistureresistant stock. Also, a considerable reduction was made in the n u m b e r of standard thicknesses and widths. The present edition of the standard covers detail requirements for six grades of "Moisture-Resistant" type and seven grades of "Exterior T y p e " Douglas fir plywood, as well as tests for those two t y p e s of bonding. For those unfamiliar with the product, a chart is included, showing the types and grades that are generally suitable for a long list of uses, and a section covering nomenclature and definitions. Printed copies of CS45-42 are obtainable from the Superintendent of Documents, Government Printing Office, Washington, D . C . The price is IO cents. MICROSCOPICAL
EXAMINATION OF PORTLAND CEMENT CLINKER.
In tile microscopical examination of portland cement clinker by the metallographic method, a prismatic phase which is readily etched by water is frequently observed. A report on the nature of this phase is presented by William C. Taylor in the April Journal of Research (RPI536). This prismatic material has been observed only in relat i v e l y rapidly cooled clinkers containing K20 or Na20, or both. However, the results of a series of phase equilibrium studies show that K2SO4 and K20.23CAO. I2SIO2 are the only compounds containing K20 that may exist when a mixture of K20, CaO, MgO, A1203, Fe203, SiO2 and SO~, in the proportions occurring in portland cement clinker, is heated and cooled under equilibrium conditions. Neither of these compounds has properties similar to those of the prismatic phase. The results of microscopical examinations by o t h e r investigators on commercial clinkers were analyzed, and these results indicated that a very close chemical relationship existed between the prismatic phase and 3 C a O .A1,O~.
528
N A T I O N A L B U R E A U OF STANDARDS N O T E S .
[J. F. 1.
Accordingly, the relation of the prismatic phase to the system K20.~aCaO. I2SiO2-CaO-sCaO-3AI=O3, and to other systems involving K20, was studied. The phase in question was found to have no range of real stability, and was produced only u n d e r conditions of r a p i d cooling. The observed thermal and compositional requirements for its formation suggest that it may be a metastable form of 3CaO.AI203 and monotropic with respect to the stable, isotropic, rectangular 3CaO'AI203. The exact composition of the prismatic phase was not established definitely because of certain experimental difficulties, which are outlined in the report. That portion of K20 combined as K2SO4 in clinker was found to have no effect in inducing the formation of the prismatic material. In conclusion, the conditions necessary for the formation of the prismatic phase are briefly set forth and it is recommended that this phase be referred to as "prismatic 3CaO.AIsOs" instead of the indefinite term, "prismatic dark interstitial material." M O D U L U S OF E L A S T I C I T Y OF C O N C R E T E .
In a recent investigation at the Bureau, Rudolph C. Valore, Jr., and Jason C. Y a t e s observed the gain in dynamic modulus of elasticity, E, of concretes made with various brands of normal, white, and high-early-strength portland cements, cured in various ways, over periods up to 635 days. They also determined the effect of calcium chloride admixtures upon this modulus over the same periods of t i m e . Two groups of 4 by 4 by 3o inch prisms were cast from a concrete proportioned I : 2 : 4 by weight and with a water content of 6~ gallons per bag of cement. In each group, for each of 8 standard, t high-early-strength, and 2 white portland cements, triplicate specimens were cast for each calcium chloride admixture content (I, and 2 per cent. by weight of cement) and for p lain concrete. Initial determinations of dynamic E were made on one group of specimens 24 hours a f t e r casting; the specimens were then placed in a moist room at 7o°F. Additional determinations were made thereafter up to.27o days, after which the specimens were placed in dry storage at constant temperature